Permanent magnet armature solenoids are well known and commercially available. Such solenoids may be used to control the air and/or fuel flow within a fuel system. With control provided by an electronic circuit, the solenoid can open and close passages carrying fuel or air to control the fuel and air mixture flow inside a diaphragm carburetor as disclosed in U.S. Pat. No. 5,611,312, the disclosure of which is incorporated herein by reference.
A solenoid elastomer tip deformable against a seat to close a passage may be molded directly to the end of the magnetic armature to ensure a sufficient seal of the passage when the solenoid is in its closed position and also to absorb the impact energy when the tip of the solenoid initially engages the seat. Conventional molding techniques require a relatively high die clamping force to mold the elastomeric tip onto the armature and this high force can deform or even fracture the brittle magnetic material of the armature. A reduction in the die clamping force results in excessive flash being formed adjacent to the elastomeric tip which requires an extra manufacturing step, which is usually performed manually, to remove the excess flash. This additional step is labor intensive and time consuming and hence, costly.
Another disadvantage of a permanent magnet armature solenoid is the limited reach, or extent to which the armature may project out of the solenoid coils. In a permanent magnet armature solenoid, there is a very close relationship between the given coil configuration and the volume of magnetic material in the armature such that if a significant portion of the armature extends beyond the coils of the solenoid, the performance of the solenoid is degraded.